Conventional techniques for wirelessly determining the location of wireless stations within a wireless communication network, such as receiving the Global Positioning System (GPS) signal from satellite radio transmissions, are often ineffective in many locations due to the weakness of the signals received and the effects of multipath signal propagation, particularly indoors and in “urban canyons” created by tall buildings, where radio signals are typically scattered by multiple objects in the environment. Such multipath scattering thwarts many conventional location techniques due to the multiple signals arriving at the terminals and network access points, e.g. base stations.
Other conventional location techniques, such as measuring the strength or time-of-arrival of signals (or differences in arrival time among multiple signals) from terrestrial transmitters are also confused by the multipath propagation and require specialized measuring apparatus in the wireless stations.
As a result, communications systems employing conventional location techniques are typically expensive, as specialized receivers or signal measuring apparatus is implemented in each wireless station. The additional reception and measurements at the wireless stations also consume additional power and consequently reduce battery lifetime. Reception of the GPS signals, for example, requires an additional antenna and receiver in a wireless station, which increases the size and weight of the station.